Method and System to Passively Align and Attach Fiber Array to Laser Array or Optical Waveguide Array

ABSTRACT

Disclosed is a method and system for passively aligning optical fibers (4), a first waveguide array (62), and a second waveguide array (42) using chip-to-chip vertical evanescent optical waveguides (44) and (64), that can be used with fully automated die bonding equipment. The assembled system (2, 30, 60) can achieve high optical coupling and high process throughput for needs of high volume manufacturing of photonics, silicon photonics, and other applications that would benefit from aligning optical fibers to lasers efficiently.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.16/316,683, filed Jan. 10, 2019, which is the United States nationalphase of International Application No. PCT/US2017/042766 filed Jul. 19,2017, and claims the benefit of U.S. Provisional Patent Application No.62/364,990 filed Jul. 21, 2016, the disclosures of which are herebyincorporated in their entirety by reference.

BACKGROUND OF THE INVENTION Field of the Invention

Disclosed herein is a system and method for optically coupling anoptical waveguide and an optical fiber.

Description of Related Art

Conventional methods of aligning and attaching a fiber or a laser to anoptical waveguide is through active alignment. A disadvantage of activealignment, however, is that it is not capable of delivering high volumethroughput and low cost manufacturing for single mode fiber and laseralignment. This is because it takes time to get all the components readyfor final assembly. Secondly, it has to deal with a total of twelve axisalignment (6 axes for each of the laser and the fiber) that finallyrequires a relatively long amount of time for alignment. Third, thelaser components have to be electrically tuned during the alignmentprocess (this is the reason why it is called “active alignment”.) Thisadds cost and time. It also introduces the uncertainty of actual laserperformance in the field as the laser may behave differently in use thanduring active alignment in a clean room environment. Finally, thealignment accuracy has to be within about 0.2 micrometers in order tomaintain high coupling efficiency for single mode fiber and laseralignment. This takes time and possibly reduces yield. It also requiressignificant care in packaging design and technique to maintain thestability of the coupling within the about 0.2 micrometer dimensionthroughout the device lifetime.

SUMMARY OF THE INVENTION

The following examples disclose an evanescent waveguide to facilitatealignment to within 1-2 micrometers; an assembly method using quiltpackaging (QP) techniques to reduce the total number of alignment axesfrom 12 to 2; and a method of assembly that is amenable to fullyautomatic pick-and-place die bonding for a high speed processing tocomplete the alignment.

Generally, provided are an improved system and method for opticallycoupling an optical waveguide and an optical fiber. In an example, theimproved system and method can use evanescent light for such opticalcoupling.

According to one preferred and non-limiting embodiment or aspect,provided is a system comprising: a first substrate having first andsecond ends, the first substrate including an optical fiber in a groove;a second substrate having first and second ends, the second substrateincluding a first waveguide having first and second ends, wherein thefirst end of the second substrate is positioned proximate to the firstend of first substrate; and a third substrate having first and secondends, the third substrate including a second waveguide having first andsecond ends. The second and third substrates are arranged with the firstends of the first and second waveguides overlapping in spaced parallelor substantially parallel relation. The first and second substrates arearranged with the second end of the second waveguide in opticalalignment with an end face of the optical fiber.

In one preferred and non-limiting embodiment or aspect, the firstwaveguide proximate the first end thereof can taper to a point, e.g., arounded point, and the second waveguide proximate the first end thereofcan taper to a point, e.g., a rounded point,.

In one preferred and non-limiting embodiment or aspect, the first endsof the first and second waveguides can overlap by 300 micrometers±30micrometers.

In one preferred and non-limiting embodiment or aspect, acenter-to-center distance between the overlapping first ends of thefirst and second waveguides can be less than or equal to 2 micrometers.

In one preferred and non-limiting embodiment or aspect, the first andsecond waveguides can be configured whereupon light propagating to thefirst end of the first or second waveguide can form an evanescent lightfield that can be received (at least in part) by the first end of theother of the first or second waveguide. The evanescent light received bythe first end of the other of the first or second waveguide canpropagate away from the first end of the other of the first or secondwaveguide.

In one preferred and non-limiting embodiment or aspect, the thirdsubstrate can overlay a part of the first substrate and a part of thesecond substrate.

In one preferred and non-limiting embodiment or aspect, the firstsubstrate can include a step having a face where the end face of theoptical fiber can be exposed. At least a part of the second end of thethird substrate can abut the face of the step of the first substrate.

In one preferred and non-limiting embodiment or aspect, the groove canbe V-shaped.

In one preferred and non-limiting embodiment or aspect, the first end ofthe first substrate can include interconnect nodules, the first end ofthe second substrate can include interconnect nodules, and theinterconnect nodules on the first end of the first substrate and thefirst end of the second substrate can be mated with each other.

In one preferred and non-limiting embodiment or aspect, the interconnectnodules on the first end of the first substrate and the first end of thesecond substrate can be mated (a) with their end faces abutting, (b) inan interdigitated manner, (c) in a friction fit manner, (d) in aninterlocking manner, or (e) some combination of (a)-(d).

In one preferred and non-limiting embodiment or aspect, eachinterconnect nodule, individually, can be flush with or extend beyond asurface of the first end of the corresponding first or second substrate.

In one preferred and non-limiting embodiment or aspect, the first endsof the first and second waveguides overlapping in spaced substantiallyparallel relation can have their longitudinal axes aligned ±2°.

In one preferred and non-limiting embodiment or aspect, the firstsubstrate can include a plurality of optical fibers, each optical fiberdisposed in a separate groove, the second substrate can include aplurality of first waveguides, and the third substrate can include aplurality of second waveguides.

In one preferred and non-limiting embodiment or aspect, a spacingbetween adjacent second waveguides can increase toward the second end ofthe third substrate.

In one preferred and non-limiting embodiment or aspect, mating alignmentfeatures can be included on at least two of the substrates, e.g., onsurfaces of the at least two substrates.

According to one preferred and non-limiting embodiment or aspect,provided is a method comprising: (a) providing a first waveguide havinga tapered end; (b) providing a second waveguide having a tapered end;(c) positioning the tapered ends of the first and second waveguideoverlapping, in an example, the first and second waveguides can overlapin spaced parallel or substantially parallel relation; (d) providing anoptical fiber positioned in optical alignment with an end of the secondwaveguide opposite the tapered end; (e) propagating light toward thetapered end of the first waveguide producing evanescent light field thatis received by the tapered end of the second waveguide; (f) propagatinglight received from the evanescent light field by the tapered end of thesecond waveguide through the second waveguide; and (g) transferring thelight propagating through the second waveguide to the optical fiber.

In one preferred and non-limiting embodiment or aspect, the tapered endsof the first and second waveguide overlapping in spaced substantiallyparallel relation can have their longitudinal axes aligned ±2°. In anexample, the optical alignment of step (d) can be within known industrytolerances for optical alignment of the axis of the optical fiber withthe axis of the end of the second waveguide opposite the tapered end.

In one preferred and non-limiting embodiment or aspect, the tapered endsof the first and second waveguide can overlap (e.g., lengthwise) by 300micrometers±30 micrometers.

In one preferred and non-limiting embodiment or aspect, the opticalfiber can be disposed on a first substrate having a first end includinginterconnect nodules, the first waveguide can disposed on a secondsubstrate having a first end including interconnect nodules, and themethod can further include positioning the interconnect nodules on thefirst ends of the first and second substrates in contact with or matingwith each other.

Further preferred and non-limiting embodiments or aspects are set forthin the following numbered clauses.

Clause 1: A system comprising: a first substrate having first and secondends, the first substrate including an optical fiber in a groove; asecond substrate having first and second ends, the second substrateincluding a first waveguide having first and second ends, wherein thefirst end of the second substrate is positioned proximate to the firstend of first substrate; and a third substrate having first and secondends, the third substrate including a second waveguide having first andsecond ends, wherein: the second and third substrates are arranged withthe first ends of the first and second waveguides overlapping in spacedparallel or substantially parallel relation; and the first and secondsubstrates are arranged with the second end of the second waveguide inoptical alignment with an end face of the optical fiber.

Clause 2: The system of clause 1, wherein: the second waveguideproximate the first end thereof can taper to a rounded point; and thesecond waveguide proximate the first end thereof can taper to a roundedpoint.

Clause 3: The system of clause 1 or 2, wherein the first ends of thefirst and second waveguides can overlap by 300 micrometers±30micrometers.

Clause 4: The system of any one of clauses 1-3, wherein acenter-to-center distance between the overlapping first ends of thefirst and second waveguides can be less than or equal to 2 micrometers.

Clause 5: The system of any one of clauses 1-4, wherein: the first andsecond waveguides can be configured whereupon light propagating to thefirst end of the first or second waveguide forms an evanescent lightfield that can be received by the first end of the other of the first orsecond waveguide; and the light from the evanescent light field receivedby the first end of the other of the first or second waveguide canpropagate away from the first end of the other of the first or secondwaveguide.

Clause 6: The system of any one of clauses 1-5, wherein the thirdsubstrate can overlay a part of the first substrate and a part of thesecond substrate.

Clause 7: The system of any one of clauses 1-6, wherein: the firstsubstrate can include a step having a face where the end face of theoptical fiber can be exposed; and at least a part of the second end ofthe third substrate can abut the face of the step of the firstsubstrate.

Clause 8: The system of any one of clauses 1-7, wherein the groove canbe V-shaped.

Clause 9: The system of any one of clauses 1-8, wherein: the first endof the first substrate can include interconnect nodules; the first endof the second substrate can include interconnect nodules; and theinterconnect nodules on the first end of the first substrate and thefirst end of the second substrate can be mated with each other.

Clause 10: The system of any one of clauses 1-9, wherein theinterconnect nodules on the first end of the first substrate and thefirst end of the second substrate can be mated (a) with their end facesabutting, (b) in an interdigitated manner, (c) in a friction fit manner,(d) in an interlocking manner, or (e) some combination of (a)-(d).

Clause 11: The system of any one of clauses 1-10, wherein eachinterconnect nodule, individually, can be flush with or extend beyond a(vertical) surface (or side) of the first end of the corresponding firstor second substrate.

Clause 12: The system of any one of clauses 1-11, wherein the first endsof the first and second waveguides overlapping in spaced substantiallyparallel relation can have their longitudinal axes aligned ±2°.

Clause 13: The system of any one of clauses 1-12, wherein: the firstsubstrate can include a plurality of optical fibers, each optical fibercan be disposed in a separate groove; the second substrate can include aplurality of first waveguides; and the third substrate can include aplurality of second waveguides.

Clause 14: The system of any one of clauses 1-13, wherein a spacingbetween adjacent second waveguides can increase toward the second end ofthe third substrate.

Clause 15: The system of any one of clauses 1-14, wherein the system canfurther include mating alignment features on at least two of thesubstrates.

Clause 16: A method comprising: (a) providing a first waveguide having atapered end; (b) providing a second waveguide having a tapered end; (c)positioning the tapered ends of the first and second waveguideoverlapping in spaced parallel or substantially parallel relation; (d)providing an optical fiber positioned in optical alignment with an endof the second waveguide opposite the tapered end; (e) propagating lighttoward the tapered end of the first waveguide producing evanescent lightthat is received by the tapered end of the second waveguide; (f)propagating evanescent light received by the tapered end of the secondwaveguide through the second waveguide; and (g) transferring the lightpropagating through the second waveguide to the optical fiber.

Clause 17: The method of clause 16, wherein the tapered ends of thefirst and second waveguide overlapping in spaced substantially parallelrelation can have their longitudinal axes aligned ±2°.

Clause 18: The method of clause 16 or 17, wherein the tapered ends ofthe first and second waveguide can overlap by 300 micrometers±30micrometers.

Clause 19: The method of any one of clauses 16-18, wherein: the opticalfiber can disposed on a first substrate having a first end includinginterconnect nodules; and the first waveguide can be disposed on asecond substrate having a first end including interconnect nodules,wherein the method can further include positioning the interconnectnodules on the first ends of the first and second substrates in contactwith or mating with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2A, and 2B show assembled (FIG. 1) and exploded perspectiveviews (FIGS. 2A and 2B) of a system for passively aligning and attachinga fiber array to a laser array or optical waveguide array;

FIG. 3A is a perspective view of isolated portions of the second andthird substrates of FIG. 1 showing the overlap and alignment of thetapered first ends of the waveguides of the second and third substrates;

FIG. 3B is a sectional view of the overlapping tapered first ends of thewaveguides of the second and third substrates shown in FIG. 3A;

FIG. 3C is a graph of efficiency (of evanescent light coupling) vs.Y-offset for the overlapping tapered first ends of the waveguides shownin FIG. 3B;

FIG. 3D is a view of an evanescent light field and coupling of theevanescent light field produced by the overlapping tapered first ends ofthe waveguides shown in FIG. 3B in response to input of laser light intoone of the waveguides;

FIG. 4 is an exploded perspective view of the pre-assembled first andthird substrates of FIG. 1;

FIG. 5 is an assembled view of the first and third substrates shown inFIG. 4;

FIG. 6 is an inverted view of the assembled first and third substratesshown in FIG. 5;

FIGS. 7A and 7B show partially assembled bottom side and top sideperspective views of the first, second, and third substrates of FIG. 1after the first and third substrates have been assembled in the mannershown in FIG. 6, and

FIGS. 8A and 8B shown bottom side and top side perspective views of thefirst, second, and third substrates shown in FIGS. 7A-7B after assembly.

DESCRIPTION OF THE INVENTION

Various non-limiting examples will now be described with reference tothe accompanying figures where like reference numbers correspond to likeor functionally equivalent elements.

For purposes of the description hereinafter, the terms “end,” “upper,”“lower,” “right,” “left,” “vertical,” “horizontal,” “top,” “bottom,”“lateral,” “longitudinal,” and derivatives thereof shall relate to theexample(s) as oriented in the drawing figures. However, it is to beunderstood that the example(s) may assume various alternative variationsand step sequences, except where expressly specified to the contrary. Itis also to be understood that the specific example(s) illustrated in theattached drawings, and described in the following specification, aresimply exemplary examples or aspects of the invention. Hence, thespecific examples or aspects disclosed herein are not to be construed aslimiting.

The following US patents are incorporated herein by reference asbackground art: U.S. Pat. Nos. 5,216,729; 4,466,696; 7,608,919;7,612,443; 8,021,965; 8,623,700; 9,243,784; 9,316,796; 8,752,283; and8,534,927.

FIGS. 1, 2A, and 2B show assembled (FIG. 1) and exploded perspectiveviews (FIGS. 2A and 2B) of a system for passively aligning and attachinga fiber array to a laser array or optical waveguide array. The systemcan include three substrates, namely, a first substrate 2 includingoptical fibers 4 disposed in grooves 6; a second substrate 30 includingwaveguides 44 formed therein or thereon by conventional waferfabrication processes; and a third substrate 60 having formed therein orthereon by conventional wafer fabrication processes waveguides 64 which,proximate one end of third substrate 60, said waveguides 64 diverge fromeach other in a fan-out arrangement.

In an example, first substrate 2 can be formed from semiconductormaterial, such as, for example, silicon, e.g., a silicon chip, thegrooves 6 can be in spaced relation, and the optical fibers 4 can be inspaced relation. For the purpose of description herein, first substrate2 will be described as being a silicon chip. However, this is not to beconstrued in a limiting sense since it is envisioned that firstsubstrate 2 can be formed of any suitable and/or desirable material thatcan be utilized and function in accordance with the intended purpose ofand in accordance with the principals described herein. In an example,grooves 6 can be in spaced parallel relation and the optical fibers 4disposed in said grooves 6 can also be in spaced parallel relation. Inan example, each groove can have the shape of a “V” that can be formedby wet chemical etching the silicon forming first substrate 2. TheV-shape can be defined by the natural (111) crystal planes of thesilicon forming first substrate 2.

In an example, first substrate 2 can include a first end 8, a second end10, a first side 12, and a second side 14. Running between first side 12and second side 14 intermediate first end 8 and second end 10, firstsubstrate 2 can include a step 16 between a higher elevation proximatesecond end 10 and a lower elevation proximate first end 8. Step 16 canbe of sufficient height whereupon end faces 18 of optical fibers 4 areexposed.

First end 8 of first substrate 2 can include a number of quilt package(QP) nodules 20, also known as interconnect nodules. QP nodules (orinterconnect nodules) are well known in the art as shown, for example,in U.S. Pat. No. 8,623,700 incorporated herein by reference.Accordingly, details regarding QP nodules and/or their formation willnot be described further herein.

The end of each QP nodule 20 facing the same direction as first end 8 offirst substrate 2 can either be flush with the surface of first end 8 orcan extend beyond (cantilevered over) the surface of first end 8.

Finally, first substrate 2 can include one or more sets of optionalalignment features 22 configured to mate, mesh, or interact with acorresponding set of optional alignment features 24 of a third substrate60 described in greater detail hereinafter.

In an example, second substrate 30 can include a first end 32, a secondend 34, a first side 36, and a second side 38. First end 32 of secondsubstrate 30 can include a number of QP nodules 40. In an example, QPnodules 40 can be arranged in a mirror image or mating pattern to QPnodules 20 of first substrate 2, whereupon when first end 8 of firstsubstrate 2 and first end 32 of second substrate 30 are broughttogether, QP nodules 20 and 40 of said substrates contact (abut) or matewith each other.

In an example, QP nodules 20 and 40 can be designed to mate. In oneexample, QP nodules 20 and 40 can be configured to mate in aninterdigitated manner. In another example, QP nodules 20 and 40configured to mate in an interdigitated matter can also be configured tofriction fit, e.g., a QP nodules 20 (or 40) can friction fit between apair of adjacent QP nodules 40 (or 20).

In yet another example, QP nodules 20 and 40 can include complimentarymating features that, in an example, can mate in an interlocking manner.For example, one or more QP nodules 20 (or 40) can include a projectionhaving a first shape/configuration and one or more QP nodules 40 (or 20)can have an aperture having a second shape/configuration that iscomplimentary to the first shape/configuration. In an example, thecomplimentary first and second shapes can couple together, for example,in a friction fit manner.

Second substrate 30 can be formed from semiconductor material, such as,for example, silicon, e.g., a silicon chip, with a surface couplingwaveguide array 42 that can include a plurality of individual waveguides44 formed in the bulk of second substrate 30. For the purpose ofdescription herein, second substrate 30 will be described as being asilicon chip. However, this is not to be construed in a limiting sensesince it is envisioned that second substrate 30 and the waveguides 44thereof can be formed of any suitable and/or desirable material that canbe utilized and function in accordance with the intended purpose of andin accordance with the principals described herein. Each waveguide 44can be a silicon-based waveguide created during the fabrication ofsecond substrate 30, in the form of a silicon chip, using conventionalsemiconductor fabrication processes known in the art. In an example, thecenter-to-center spacing between adjacent pairs of waveguides 44 can bebetween 10-20 micrometers. However, this is not to be construed in alimiting sense. In an example, the center-to-center spacing betweenadjacent pairs of waveguides 44 are the same within some predeterminedtolerance, e.g., ±0.5 micrometers. However, this is not to be construedin a limiting sense.

In an example, waveguides 44 can be positioned in spaced relation andcan extend between first end 32 and second end 34 of second substrate30, with each waveguide 44 including a first end 46 and a second end 48.In an example, first end 46 of each waveguide 44 can be spaced adistance D from first end 32 of second substrate 30. In another example,the first end 46 of each instance of waveguide 44 can be spaced adifferent distance from first end 32.

In an example shown in FIG. 2A, the second end 48 of each waveguide 44can be coupled to a laser 50 formed in second substrate (formed of, forexample, silicon) using semiconductor fabrication processes known in theart. Each laser 50 can be excited with electrical energy supplied, forexample, via a bonding pad 52 (shown) or a QP nodule (not shown) in amanner known in the art to produce said laser light. Laser lightproduced by each laser 50 can propagate from second end 48 toward firstend 46 of the corresponding waveguide 44. In another example, each laser50 can be mounted on second substrate 30. Where lasers 50 are mounted onsecond substrate 30, electrical energy can optionally be supplieddirectly to said lasers thereby avoiding the need for a bonding pad andrelated electrical interconnects to be formed on second substrate 30.

FIG. 2B shows another example which is similar in most respects to theexample shown in FIG. 2A except that lasers 50, bonding pads 52, andrelated interconnects are omitted and replaced with a coupler orcouplers 55 between the second ends 48 of waveguides 44 and off-boardlasers 57 which are coupled to said waveguides 44 via optical fibers 59and coupler or couplers 55.

The use of a coupler or couplers 55 to couple optical fibers 59 towaveguides 44 is well known in the art. In one non-limiting example,coupler or couplers 55 can be an external grating-structured collimatinggradient-index (GRIN) lens wherein laser light emerging from an opticalfiber 59 is expanded and collimated by the GRIN lens. The exit face ofthe GRIN lens is disposed at an angle relative to the propagationdirection of the laser light and is polished and structured with ahigh-frequency grating. When the exit face of the collimating lens ofcoupler or couplers 55 is placed in close proximity or in contact with asurface of a waveguide 44, a part of the collimated laser light beam canbe coupled to and guided by said waveguide 44. The description ofcoupler or couplers 55 as being a GRIN lens is not to be construed in alimiting sense since it is envisioned that any suitable and/or desirablecoupler or couplers 55 known in the art or hereinafter developed can beused to couple laser light from an optical fiber 59 to a waveguide 44.

The first end 46 of each waveguide 44 can include a laser sink (notshown) for receiving laser light input into second end 48 of saidwaveguide 44 in order to dissipate said laser light and the heatproduced thereby.

Third substrate 60 can be made from glass, silicon nitride on silicon,polymer, or any other suitable and/or desirable optical grade material.Third substrate 60 can include a waveguide array 62 that includes aplurality of waveguides 64 formed thereon in a manner known in the art.Each waveguide 64 includes a first end 66 and a second end 68.

Each waveguide 64 of waveguide array 62 can extend from a first end 70of third substrate 60 toward a second end 72 of third substrate 60. Inan example, a first part 74 of waveguide array 62 proximate first end 70includes a number of waveguides 64 in spaced relation. In an example,the plurality of waveguides 64 along first part 74 of waveguide array 62can be in spaced parallel relation.

In an example, a second part 76 of waveguide array 62 proximate secondend 72 can include the plurality of waveguides 64 in a fan-like pattern,wherein the spacing between adjacent waveguides 64 increases from firstpart 74 toward second end 72.

In an example, the center-to-center spacing between adjacent pairs ofoptical fibers 4 of first substrate 2 is between 125-250 micrometers;the center-to-center spacing between adjacent pairs of waveguides 44 ofsecond substrate 30 is between 10-20 micrometers; the center-to-centerspacing between adjacent pairs of waveguides 64 along the first part 74of waveguide array 62 is between 10-20 micrometers; and thecenter-to-center spacing between adjacent pairs of waveguides 64 atsecond end 72 of third substrate 60 is between 125-250 micrometers.However, the foregoing dimensions are not to be construed in a limitingsense since it is envisioned that the center-to-center spacing betweenadjacent pairs of optical fibers 4, waveguides 44, and waveguides 64(including the spacing proximate first part 74 and second part 76 ofwaveguide array 62) can be chosen to be any suitable and/or desirabledimension consistent with the intended purpose of and in accordance withprincipals for the first through third substrates 2, 30, and 60described herein. For example, the center-to-center spacing of each pairof adjacent waveguides 44 and each pair of adjacent waveguides 46 can bethe same as the center-to-center spacing of optical fibers 4. Hence, inthis example, the fan-out of the waveguides 64 of the second part 76 ofwaveguide array 62 proximate second end 72 can be omitted.

In the completed assembly of the system shown in FIG. 1, first end 8 offirst substrate 2 and first end 32 of second substrate 30 can be abuttedtogether or can be in spaced relation (the latter occurring when one ormore of QP nodules 20 and 40 extend in a cantilevered manner beyond theface of first end 8 of first substrate 2 and the face of first end 32 ofsecond substrate 30, respectively) with one or more QP nodules 20abutting or mating with one or more corresponding QP nodules 40. In anexample, optional alignment features 22 of first substrate 2 andoptional alignment features 24 of third substrate 60 can be matingalignment features that facilitate accurate alignment of third substrate60 to first substrate 2 and second substrate 30. In an example, the setof alignment features 24 can be one or more pillars or posts and the setof alignment features 22 can be a set of mating apertures, each of whichis configured to receive at least one pillar or post. In an example, thepillars or posts can be formed of a metal, such as, without limitation,copper. However, this is not to be construed in a limiting sense sinceit is envisioned that alignment features 22 and 24 can be formed of anysuitable and/or desirable material and alignment features 22 and 24 canbe of any suitable and/or desirable form, shape, or design thatfacilitate alignment of first substrate 2 and third substrate 60.

In an example, at least the lower part (in the view shown in FIGS. 1,2A, and 2B) of second end 72 of third substrate 60 can abut the verticalface of step 16 of first substrate 2 when third substrate 60 is matedwith first substrate 2.

In the example finished assembly shown in FIG. 1, the surface of thirdsubstrate 60 that includes waveguide array 62 formed therein can bridgethe abutment or spaced relation of first end 8 of first substrate 2 andfirst end 32 of second substrate 30. Also, at least portions of thewaveguides 64 of first part 74 of waveguide array 62 can be in verticalor substantially vertical alignment positioned over at least portions ofthe waveguides 44 of waveguide array 42 proximate first end 32 of secondsubstrate 30. The face of one or more waveguides 64 of waveguide array62 at second end 68 of third substrate 60 can be aligned with or inoptical alignment with, e.g., abutting or in spaced relation with, oneor more end faces 18 of optical fibers 4 in grooves 6 of first substrate2. In an example, the face at the second end 68 of each waveguides 64can be aligned with or in optical alignment with an end face 18 of asingle optical fiber 4 in a groove 6.

An example use of the system shown in FIG. 1 will now be described. Forsimplicity, the use of a single laser 50 or 57 outputting laser lightdown a single waveguide 44 and the response thereto of a waveguide 64 invertical or substantially vertical alignment with said waveguide 44, andthe response of an optical fiber 4 in alignment with a second end 68 ofsaid waveguide 64 will be described. However, this is not to beconstrued in a limiting sense.

In response to a laser 50 or 57 outputting laser light into a second end48 of a waveguide 44, said laser light propagates along waveguide 44 andevanescent light is produced laterally to the axis of waveguide 44proximate first end 46 of said waveguide 44. This evanescent light isreceived, at least in part, by a waveguide 64, proximate first end 66 ofsaid waveguide 64, in vertical or substantially vertical alignment withsaid waveguide 44. The evanescent light received in waveguide 64propagates in waveguide 64 from first end 66 to second end 68 of saidwaveguide 64. Light travelling in waveguide 64 exits second end 68 ofwaveguide 64 and is received in the end face 18 of an optical fiber 4aligned with, in an example, abutted against, or in optical alignmentwith second end 68 of waveguide 64. Light entering the face 18 ofoptical fiber 4 propagates in said optical fiber 4 in a direction towardsecond end 10 of first substrate 2 for use in a system (not shown)coupled to the end of optical fiber 4 opposite face 18 of optical fiber4. Hence, as can be seen, laser light output by a laser 50 or 57propagates to an end of an optical fiber 4 proximate second end 10 offirst substrate 2 via a waveguide 44 and a waveguide 64 in vertical orsubstantially vertical alignment with said waveguide 44.

It is estimated that the coupling efficiency between a waveguide 64 invertical or substantially vertical alignment with a waveguide 44 can begreater than 90% when said waveguides 44 and 64 are within onemicrometer of each other, and greater than 73% when said waveguides 44and 64 are within two micrometers of each other. In an example, theforegoing coupling efficiencies were modeled for a waveguide 44 and awaveguide 64 in spaced vertical alignment with each other separated by acenter-to-center distance of one micrometer for coupling efficiencygreater than 90%, and a center-to-center distance of two micrometers forcoupling efficiency greater than 73%.

The following Table 1 shows examples of measured average TE and TMinsertion losses (in dB) at various interface locations of an actualassembled system of the type shown in FIG. 1.

TABLE I Average Insertion Loss in dB [λ = 1500-1600 nm] TE- TM- TE IndexTM Index TE TM Interface (SiN—SiN) Match (SiN—SiN) Match (SiN—Si)(SiN—Si) Butt-Coupling interface of a −0.99 −0.99 −0.66 −0.69 −0.99−0.61 fiber 4 to a waveguide 64 at step 16 of first substrate 2 QPNodule Gap—where first −0.06 −0.00 −0.68 −0.13 −0.06 −0.61 end 8 offirst substrate 2 abuts or is spaced from first end 32 of secondsubstrate 30 Evanescent Coupling between −0.29 −0.29 −0.39 −0.46 −0.2−0.24 a waveguide 64 and a waveguide 44 TOTAL [dB]: −1.34 −1.28 −1.73−1.29 −1.25 −1.46

In an example, to help reduce insertion loss, index matching materialknown in the art can be disposed at (1) the interface (or butt-coupling)of a fiber 4 to a waveguide 64 by step 16 and/or (2) where first end 8of first substrate 2 abuts or is spaced from first end 32 of secondsubstrate 30.

In an example, the largest lateral dimension of waveguide 44 can be thesame as the largest lateral dimension of the portion of waveguide 64 invertical or substantially vertical alignment with said waveguide 44.Moreover, in an example, the shape of the second end 68 of eachwaveguide 64 at second end 72 of third substrate 60 can be circular inshape to match the circular shape of the core of the end face 18 of theoptical fiber 4 aligned with, and desirably abutted, against the secondend 68 of waveguide 64. The shape-matching of the aligned end faces ofoptical fiber 4 and waveguide 64 facilitates coupling between opticalfibers 4 and waveguides 64.

Regarding the shape of waveguide 44 between first part 74 of waveguidearray 62 and second part 76, the portion of each waveguide 64 formingsecond part 76 of waveguide array 62 can change shape and dimensionsbetween the transition between first part and second part 74, 76 ofwaveguide array 62 and second end 72 of third substrate 60. In otherwords, moving from first part 74 of waveguide array 62 toward second end72 of third substrate 60, each waveguide 64 can change shape and/ordimensions to facilitate the transition between the shapes of waveguides44 of waveguide array 42 and optical fibers 4 of first substrate 2.

Having thus described the example systems shown in FIGS. 1, 2A, and 2B,an example method of assembling first, second, and third substrates 2,30, and 60 into the assembled system shown in FIG. 1 will now bedescribed with reference to FIGS. 4-8B. It is to be appreciated,however, that the following description is exemplary only and is not tobe construed in a limiting sense.

With reference to the exploded perspective view shown in FIG. 4, in anexample, first substrate 2 and third substrate 60 can be joined with atleast the lower portion (in the perspective view shown in FIG. 4) ofsecond end 72 of third substrate 60 abutted against the vertical face ofstep 16 of first substrate 2 and with second ends 68 of waveguides 64aligned with, and, in an example, abutting end faces 18 of opticalfibers 4.

In an example, to facilitate this alignment between second ends 68 ofwaveguides 64 and end faces 18 of optical fibers 4, waveguides 64 can bepositioned on or in the downward facing surface of third substrate 60 inthe perspective view shown in FIG. 4.

Optional alignment features 22 and 24 can be provided on first substrate2 and third substrate 60 as an aid in aligning the second ends 68 ofwaveguides 64 to the end faces 18 of optical fibers 4 at step 16.

In an example, a high precision die bonder can acquire third substrate60 from a carrier pack and invert it so that the surface of thirdsubstrate 60 where waveguide array 62 is formed faces downward. The diebonder can also pick-up first substrate 2, including one or more grooves6 and, in an example, one or more optical fibers 4 in said one or moregrooves 6, and place it on a heating stage as a substrate to receivethird substrate 60. The die bonder can then transfer third substrate 60on top of first substrate 2 as shown in FIG. 4 to produce the assembly2, 60 shown in the assembled perspective view of FIG. 5.

First substrate 2 including third substrate 60 positioned thereon in themanner shown in FIG. 5 can be bonded together in any suitable and/ordesirable manner known in the art. In an example, the set of alignmentfeatures 24 and the set of alignment features 22 can be made ofmaterials having a low eutectic point, whereupon heating the assemblyshown in FIG. 5 can bond first and third substrates 2, 60 together inthe manner shown in FIG. 5. In another example, epoxy can be dispensedbetween the mating surfaces of first and third substrates 2, 60,desirably away from waveguide array 62 and step 16. This epoxy can thenbe subsequently cured in any suitable and/or desirable manner, e.g., byexposure to UV light, when a UV curable epoxy is used, or by theapplication of heat, when a heat curable epoxy is used.

With reference to the assembled perspective view of FIG. 6, the assemblyof the first and third substrates 2 and 60 shown in FIG. 5 can theninverted whereupon the waveguides 64 of waveguide array 62 of thirdsubstrate 60 face upward, as shown in FIG. 6.

FIGS. 7A and 7B show partially assembled bottom side and top sideperspective views of first, second, and third substrates 2, 30, and 60,respectively, after first and third substrates 2 and 60 have been joinedin the manner shown in FIGS. 5 and 6. As shown in FIGS. 7A and 7B, firstend 32 of second substrate 30 (with the surface that includes waveguidearray 42 facing down in the view shown in FIG. 7A) is moved intoposition abutting or in spaced relation to first end 8 of firstsubstrate 2 with QP nodules 40 and 20 of second and first substrates 30and 2, respectively, in contact and/or mating, and with waveguides 44 ofwaveguide array 42 in vertical or substantially alignment withwaveguides 64 of waveguide array 62. Herein, “vertical or substantiallyvertical alignment” means alignment of waveguides 64 and waveguides 44in the Z direction shown in the Cartesian coordinate system diagram 90shown in FIG. 1 within ±2 micrometers off vertical in the Y direction orwithin ±5° of vertical.

Bottom side and top side perspective views of the completed assembly offirst, second, and third substrates 2, 30, and 60 are shown in FIGS. 8Aand 8B, respectively.

Equipment utilized to assemble first, second, and third substrates 2,30, and 60 can include any suitable and/or desirable equipment currentlyknown in the art or developed hereinafter. In an example, die bondersincluding suitable chucks or stages can be utilized to pick, maneuver,orient, and place substrates 2, 30, and 60 to form the assembly shown inFIGS. 8A and 8B.

Referring back to FIGS. 1, 2A, and 2B, as can be seen, the completedassembly of first, second, and third substrates 2, 30, and 60 includesfirst end 8 of first substrate 2 abutting or in spaced relation withfirst end 32 of second substrate 30, with QP nodules 20 and 40 incontact or mating. In an example, QP nodules 20 and 40 aid incontrolling angular variations and alignment along the length (or X)direction of waveguides 44 of waveguide array 42 and waveguides 64 ofthe first part 74 of waveguide array 62.

The surface of third substrate 60 including at least a portion of thesecond part 76 of waveguide array 62 is in contact with the stepped-downor lower surface of first substrate 2, i.e., the surface of firstsubstrate 2 that does not include optical fibers 4 and grooves 6,proximate first end 8. At the same time, the surface of third substrate60 that includes at least a portion of the first part 74 of waveguidearray 62 is in contact with the surface of second substrate 30 thatincludes at least a portion of waveguide array 42 proximate first end 32of second substrate 30.

In the example shown in FIG. 1, the surface of third substrate 60 thatincludes waveguide array 62 is covered by or covers portions of firstand second substrates 2 and 30. In contrast, only the portions of firstand second substrates 2 and 30 proximate QP nodules 20 and 40 arecovered by or cover the surface of third substrate 60.

The example of assembling first, second, and third substrates 2, 30, and60 discussed above in connection with FIGS. 4-8B is not to be construedin a limiting sense since it is envisioned that said substrates can beassembled to the form shown in FIGS. 8A and 8B in any suitable and/ordesirable manner. In an example, first end 8 of first substrate 2 andfirst end 32 of second substrate 30 can be abutted together or fixed inspaced relation with OP nodules 20, 40 abutting followed by placement ofthird substrate 60 over first substrate 2 abutted to or in spacedrelation to second substrate 30 in the manner shown in FIG. 1.

The assembly of first, second, and third substrates 2, 30, and 60 can bebonded together in any suitable and/or desirable manner In an example,an epoxy (UV curable or heat curable) can be utilized. In an example, anepoxy can be disposed between the facing surfaces of first substrate 2and third substrate 60, and between the facing surfaces of secondsubstrate 30 and third substrate 60 in the assembled view shown in FIGS.1, 8A, and 8B. In an another example, thermal surface bonding can beutilized to join first, second, and third substrates 2, 30, and 60 viapre-deposited layers of, for example, SiO² on each substrate. In yetanother example, laser-assisted soldering can be utilized to join first,second, and third substrates 2, 30, and 60. Combinations of thermalsurface bonding via pre-deposited layers (such as SiO²), epoxy (UV orheat curable), and or laser-assisted soldering can also be utilized tojoin first, second, and third substrates 2, 30, and 60 in the mannershown in FIGS. 1, 8A, and 8B.

Referring now to FIGS. 2A, 2B, and 3A-3D, approaching first end 32 ofsecond substrate 30, the material forming each waveguide 44 can taperfrom a full lateral width (in the Y direction) to a rounded point 54(FIG. 3A) at first end 46 of said waveguide 44. Similarly, proximatefirst end 66, each waveguide 64 can be tapered and have a rounded point78. Moving in a direction away from first end 66, waveguide 64 can taperoutwardly to its full lateral width (in the Y direction) for theremainder of first part 74 of waveguide array 62 (FIG. 3A).

In an example, each waveguide 44 proximate first end 46 thereof and eachwaveguide 64 proximate first end 66 thereof in vertical or substantiallyalignment with said waveguide 44 can overlap each other by 300micrometers±30 micrometers (FIG. 3B). This overlap is shown in FIG. 3Bby reference number 80. However, this is not to be construed in alimiting sense.

In an example, the lateral width (in the Y direction shown in FIG. 3A)of the tapered part of waveguide 44 25-100 micrometers away from the tipof rounded point 54 can be less than ½ or ¼ of the largest width in theY direction of the body of waveguide 44 away from the tapered part ofwaveguide 44. In another example, the lateral width (in the Y directionshown in FIG. 3A) of the tapered part of waveguide 64 25-100 micrometersaway from the tip of rounded point 78 of waveguide 64 can be less than ½or ¼ of the largest width in the Y direction of the body of waveguide 64away from the tapered part of waveguide 64. In other words, the width(in the Y direction) of the un-tapered portion of waveguide 44 can be2-4 times greater than the width (in the Y direction) of the taperedpart of waveguide 44 25-100 micrometers way from the tip of roundedpoint 54. In another example, the width (in the Y direction) of theun-tapered portion of waveguide 64 can be 2 or 4 times greater than thewidth (in the Y direction) of the tapered part of waveguide 64 25-100micrometers way from the tip of rounded point 78.

In an example, the largest thickness (or height) of waveguide 44 in theZ direction (shown in FIG. 3A) is b 1.25 micrometers and the largestthickness (or height) of waveguide 64 in the Z direction is 200nanometers. However, this is not to be construed in a limiting sense.

The tapered portion of each waveguide 44 facilitates the formation of anevanescent light field in response to laser light propagating inwaveguide 44 towards first end 46. When the tapered portion of awaveguide 64 is positioned in vertical or substantially verticalalignment (Z) alignment (±2 micrometers off vertical in the Y direction)with the tapered portion of waveguide 44, and with the longitudinal axesof waveguides 46 and 64 parallel or substantially parallel, ±2° ofparallel, the evanescent light field can be received in the taperportion of waveguide 64 proximate first end 66 thereof for continuedpropagation of the received light to second end 68 of waveguide 64 fortransfer to an optical fiber 4 having an end face 18 aligned with saidsecond end 68.

As can be seen, disclosed is a method and system for passively aligningoptical fibers 4, waveguide array 62, and waveguide array 42 usingchip-to-chip vertical evanescent optical waveguides 44 and 64, that canbe used with fully automated die bonding equipment. It is expected thatthe assembly 2, 30, and 60 can achieve high optical coupling and highprocess throughput for needs of high volume manufacturing of photonics,silicon photonics, and other applications that need to align opticalfibers to lasers efficiently.

Also disclosed herein is a system comprising: a first substrate havingfirst and second ends, the first substrate includes an optical fiber ina groove; a second substrate having first and second ends, the secondsubstrate includes a first waveguide having first and second ends,wherein the first end of the second substrate is positioned proximate tothe first end of first substrate; a third substrate having first andsecond ends, the third substrate includes a second waveguide havingfirst and second ends, wherein: the second and third substrates arearranged with the first ends of the first and second waveguidesoverlapping in spaced parallel or substantially parallel relation; andthe first and second substrates are arranged with the second end of thesecond waveguide in optical alignment with an end face of the opticalfiber.

The second waveguide proximate the first end thereof can taper to apoint, e.g., a rounded point. The second waveguide proximate the firstend thereof can taper to a point, e.g., a rounded point.

The first ends of the first and second waveguides can overlap by 300micrometers±30 micrometers.

A center-to-center distance between the overlapping first ends of thefirst and second waveguides can be less than or equal to 2 micrometers.

The first and second waveguides can be configured whereupon lightpropagating to the first end of the first or second waveguide forms anevanescent light field that can be received by the first end of theother of the first or second waveguide. The evanescent light fieldreceived by the first end of the other of the first or second waveguidecan propagate away from the first end of the other of the first orsecond waveguide.

The third substrate can overlay a part of the first substrate and a partof the second substrate.

The first substrate can include a step having a face where the end faceof the optical fiber can be exposed. At least a part of the second endof the third substrate can abut the face of the step of the firstsubstrate.

The groove can be V-shaped.

The first end of the first substrate can include interconnect nodules.The first end of the second substrate can include interconnect nodules.The interconnect nodules on the first end of the first substrate and thefirst end of the second substrate can be mated with each other.

The interconnect nodules on the first end of the first substrate and thefirst end of the second substrate can be mated (a) with their end facesabutting, (b) in an interdigitated manner, (c) in a friction fit manner,in (d) an interlocking manner, or some combination of (a)-(d).

Each interconnect nodule, individually, can be flush with or extendbeyond a surface of the first end of the corresponding first or secondsubstrate.

The first ends of the first and second waveguides can overlapping inspaced substantially parallel relation can have their longitudinal axesaligned ±2°.

The first substrate can include a plurality of optical fibers, eachoptical fiber disposed in a separate groove. The second substrate caninclude a plurality of first waveguides. The third substrate can includea plurality of second waveguides.

A spacing between adjacent second waveguides can increase toward thesecond end of the third substrate.

At least two of the substrates can include mating alignment features.

Also disclosed herein is a method comprising: (a) providing a firstwaveguide having a tapered end; (b) providing a second waveguide havinga tapered end; (c) positioning the tapered ends of the first and secondwaveguide overlapping in spaced parallel or substantially parallelrelation; (d) providing an optical fiber positioned in optical alignmentwith an end of the second waveguide opposite the tapered end; (e)propagating light toward the tapered end of the first waveguideproducing evanescent light that is received by the tapered end of thesecond waveguide; (f) propagating evanescent light received by thetapered end of the second waveguide through the second waveguide; and(g) transferring light propagating through the second waveguide to theoptical fiber.

The tapered ends of the first and second waveguide overlapping in spacedsubstantially parallel relation can have their longitudinal axes aligned±2°. In an example, the optical alignment of step (d) can be withinknown industry tolerances for optical alignment of the axis of theoptical fiber with the axis of the end of the second waveguide oppositethe tapered end.

The tapered ends of the first and second waveguide can overlap by 300micrometers±30 micrometers.

The optical fiber can be disposed on a first substrate and can have afirst end including interconnect nodules. The first waveguide can bedisposed on a second substrate that can have a first end includinginterconnect nodules. The method can further include positioning theinterconnect nodules on the first ends of the first and secondsubstrates in contact with or mating with each other.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it is to be understood thatthe present invention contemplates that, to the extent possible, one ormore features of any embodiment can be combined with one or morefeatures of any other embodiment.

The invention claimed is:
 1. A method comprising: (a) providing a firstwaveguide having a tapered end; (b) providing a second waveguide havinga tapered end; (c) positioning the tapered ends of the first and secondwaveguide overlapping in spaced parallel or substantially parallelrelation; (d) providing an optical fiber positioned in optical alignmentwith an end of the second waveguide opposite the tapered end; (e)propagating light toward the tapered end of the first waveguideproducing evanescent light that is received by the tapered end of thesecond waveguide; (f) propagating evanescent light received by thetapered end of the second waveguide through the second waveguide; and(g) transferring the light propagating through the second waveguide tothe optical fiber.
 2. The method of claim 1, wherein the tapered ends ofthe first and second waveguide overlapping in spaced substantiallyparallel relation have their longitudinal axes aligned ±2°.
 3. Themethod of claim 1, wherein the tapered ends of the first and secondwaveguide overlap by 300 micrometers±30 micrometers.
 4. The method ofclaim 1, wherein: the optical fiber is disposed on a first substratehaving a first end including interconnect nodules; and the firstwaveguide is disposed on a second substrate having a first end includinginterconnect nodules, wherein: the method further includes positioningthe interconnect nodules on the first ends of the first and secondsubstrates in contact with or mating with each other.